The present invention relates to a procedure for maximizing the visual quality of an image as defined in the claims.
In addition, the present invention relates to an apparatus for maximizing the visual quality of an image as defined in the claims.
As the use of information networks is gaining ground and their data transmission capacity is increasing, increasing numbers of digital colour images are being transmitted across the networks. Images are sent into the network from various sources, using different equipment and various encoding and packing methods known in themselves. Moreover, the technical origin of the images is generally unknown to the receiver.
Due to errors caused by the operations performed on the image, such as encoding and packing, as well as errors generated in the data transfer medium, the visual quality of the image is often deteriorated as compared with its original visual quality. For this reason, methods for implementing the colour reproduction of an image have been developed to maximize the visual quality of the image. In an optimal case, the reproduced image reproduces the visual impression given by an error-free original image unchanged. In practice, however, this is not always possible. A basic reason for this is that the original image usually has a larger range of colours than is possible to reproduce. But even if all the colours in the original could be reproduced, creating a visual similarity would still be difficult. That is to say, current chromatics does not know any methods for quantitatively determining the colour impressions produced by normal images consisting of numerous fields of different colours and shapes.
Several methods for colour correction and calibration, for improving the visual quality of an image, are known in the art. A feature common to these methods is that the technical origin of the image is known or a "model" (a high-quality photograph) of the image exists. However, the technical origin of an image received e.g. over an information network is not known, and therefore the prior-art methods cannot be used to improve the visual quality of the image.
It is possible to improve the visual quality of an image by a manual method, whereby an operator processing the image makes observations about the original picture, an image displayed on a computer screen or printed out on a printer, and corrects the colour reproduction manually on the basis of his/her own observations and skill. However, processing an image by this manual method is a slow and laborious business and requires a skilled image processing operator. Moreover, manual image processing requires expensive machines which must be compatible with each other and calibrated to ensure e.g. that an image displayed on-screen visually corresponds to its printed copy.